Shielded antenna



Jan. 4, 1966 D. J. MOORE SHIELDED ANTENNA Filed June 11, 1965 Jill.'

MA, 47k

BAV/D Cl. M0095,

United States Patent O 3,228,030 SHlELDED ANTENNA David J. Moore,Ontario, Calif., assigner to General Dynamics Corporation, Pomona,Calif., a corporation of Delaware Filed June 11, 1965, Ser. No. 463,1105 Claims. (Cl. 343-746) This invention relates to antenna systems andmore particularly to a slot form of antenna particularly useful forradiation of microwave energy.

Early microwave antenna systems required expensive conductor systemsemploying waveguides or coaxial cables. As technical development hasreached into higher and higher frequencies, the precision requirementsof these types of radiation systems have become very exacting, therebyrendering ditiicult the manufacture of satisfactory microwave antennas.

As technology advanced, microwave antenna systems were developed of acharacter readily adapted for use of printed circuit techniques. Thisprinciple, as exemplified by US. Patent No. 2,654,842, employs as theradiating element of the antenna system a conductor, known commonly as aline conductor, which is small in width compared with a secondconductor, known commonly as a grounded conductor. The conductors arespaced apart by a dielectric. By making the ground conductorconsiderably wider than the line conductor, an image 'effect is producedwhich provides in effect an electric and magnetic field distributionbetween the two conductors. The width of the line and the spacingbetween the line and the ground conductor. The conductors are spacedapart of the transmission path.

The antenna of the present invention is basically a two element antennawhich has a flat tank coil sandwiched close to a iiat plane Faradayshield. This antenna can be used in a small package for transmitting andreceiving RF signals. The antenna is shielded and minimizes detuningeffect when placed next to a non-ferrous body.

The antenna of this invention is particularly adapted for use withtelemetry equipment for monitoring the functions of living bodies. Insuch applications, signals generated by the body are received andtransmitted by the instant antenna to a receiver such as a signal meteror oscilloscope where the body functions can be viewed to determine anyabnormal reactions or conditions.

Also, this antenna has utilization in communication systems carried onor by a living being due to the shielded arrangement which minimizesdetuning effect due to the nearness of such a non-ferrous body.

Therefore, it is an object of this invention to provide an antenna.

A further object of the invention is to provide a shielded antennacapable of efficient operation when located next to a non-ferrous body.

Another object of the invention is to provide a coil antenna shielded tominimize detuning eiect when placed next to a living body.

Another object of the invention is to provide a two element antennahaving a llat tank coil sandwiched close to a flat plane Faraday shieldhaving a T-slot configuration.

Another object of the invention is to provide a shielded antenna whereinthe shield is configured to reduce possibilities of changing theoscillating frequency due to being contacted by a non-ferrous body.

Other objects of the invention will become readily apparent from thefollowing description and accompanying drawings wherein:

FIG. l is a view showing the T-slot shield of the antenna of thisinvention;

FIG. 2 is a view showing the fiat coil of the antenna;

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FIG. 3 is an end view illustrating the shield and at coil separated by adielectric; and

FIG. 4 is a schematic illustrating a typical transmitter circuit for theantenna of this invention.

Broadly, the present invention relates to a shielded antenna comprisinga thin sheet of dielectric material sandwiched between a printed circuittank coil on one side and a grounded Faraday shield having a T-slot onthe other side.

Referring now to the drawings, FIGS. 1 to 3 illustrate a two elementantenna which has a flat tank coil 10 sandwiched close to a at planeFaraday shield 11 by dielectric material 12, the shield 11 beingprovided with a Tshaped slot 13. If desired a jumper 14 may be used toadjust the self-resonant point of the antenna. The proper selection ofthe dielectric, however, eliminates the need of jumper 14. The shieldedantenna, for example, may be printed on a double copper clad controlleddielectric board with the coil 10 printed on one side and the shield 11printed on the other, the dielectric 12 being Epon glass which isessentially an epoxy-type resin impregnated fiber glass material, theresin being of the laminating type lproduced by Shell ChemicalCorporation under the trade name Epon.

The embodiment of the antenna illustrated is designed to be used in a 7channel pulse width modulated telemetry unit for monitoring biomedicalsignals. The unit was built for a frequency of operation from 60 to 110mc. The tank coil type antenna provides effective operation inapplications having space limitations such as biomedical telemetryunits.. The proximity effect of a body close to an unshielded tank coil10 changes the oscillating frequency proportionally to the distancebetween the coil and the body. The Faraday shield 11 maintains aconstant oscillating frequency even though there is a large non-ferrousbody near by.

The antenna illustrated has a dielectric 12 yof Epon glass and athickness of 0.125 inch. If a thinner board is used the distributedcapacitance between the coil 10 and the shield 11 increases, and the Qof the antenna reduces to a value too low for good radiation. A thickerboard will reduce the shielding effect of the Faraday shield.

The T-slot 13 in the shield 11 of the antenna increases the Q andradiation effect of the antenna compared to an unslotted shield, or ashield of' a different slot configuration. The T-slot shield may betouched by a hand anywhere on the shield, except on the stem of the Twithout changing the oscillating frequency. The reason for the eicientoperation of the T-slot 13 is not understood at the present time.However, tests have shown that this preferred configuration operates asset forth above.

The length of the printed coil l0 is determined by the type of epoxyboard used and should be of such length that the antenna will beself-resonant at a frequency just higher than the highest frequency ofthe tuning range. The self-resonant point can be adjusted by the jumper14, as pointed out above.

The operation of the transmitter circuit illustrated in FIG. 4 will beapparent to those skilled in the art and a detailed explanation of thecircuit is deemed unnecessary. The values of the circuit components areexemplary only and correspond to the specific values for the antenna setforth above.

It has thus been shown that the present invention provides an antennathat can be used in a small package for transmitting and receiving RF.signals, the antenna being shielded to minimize detuning elect whenplaced next to a non-ferrous body, such as a human being. Thus, theantenna has particular application in telemetry units for monitoringbiomedical signals or in wireless microphones.

` Whilea specific example of the invention has been illustrated anddescribed, modifications will become apparent to those skilled in theart, and it is intended to ycover in the appended claims all suchmodificati-ons as come within the spirit and scope of this invention.

What I claim is:

1. A shielded antenna comprising a thin sheet of dielectric materialsandwiched between a printed circuit tank coil on 'one side and agrounded Faraday shield on the other side, said shield having a T-shapedslot therein.

2. The shielded antenna diened in claim 1, additionally including ajumper member operably connected with said tank coil for adjusting theself-resonant point of the antenna.

3. The shielded antenna defined in claim 1, wherein said dielectricmaterial is composed of epoxy impregnated iiber glass and said tank coiland shield are copper.

4. The shielded antenna defined in claim 1, wherein said dielectricmaterial, said tank coil, and said shield have a combined thickness ofabout 0.125 inch.

S. In combination with a telemetry unit for monitoring biomedicalsignals, an antenna comprising dielectric material with a llat tank coiland a at plane shield operative- 1y positioned on opposite sidesthereof, said shield being provided with a T-shaped slot therein forminimizing the 2 detuning elect Ion the antenna when placed next to anon-ferrous body.

4 References Cited by the Examiner UNITED STATES PATENTS 2,654,84210/1953 Engelmann 343--770 3,049,711 8/1962 Hooper 343-856 X 3,133,5375/1964 Muth 325-1l8 X References Cited by the Applicant UNITED STATESPATENTS 2,586,854 2/ 1952 Myers. 2,654,842 10/ 1953 Engelmann. 2,874,2762/ 1959 Dukes et al. 2,929,065 3/ 1960 Kreinheder. 2,990,547 6/ 1961McDougal. 3,110,030 1l/1963 C-ole. 3,135,960 6/1964 Kaiser.

OTHER REFERENCES J. A. McDonough, R. G. Malech, and J. Kowalsky:Developments in Printed Antenna Design, Electronic Design, June 1, 1957,pages 42-45.

E. L. Klein: Printed Circuit Antennas, CQ, Iuly 1958, pages 28-31.

ELI LIEBERMAN, Acting Primary Examiner.

1. A SHIELDED ANTENNA COMPRISING A THIN SHEET OF DIELECTRIC MATERIALSANDWICHED BETWEEN A PRINTED CIRCUIT TANK COIL ON ONE SIDE AND AGROUNDED FARADAY SHIELD ON THE OTHER SIDE, AND SHIELD HAVING A T-SHAPEDSLOT THEREIN.